Sorry, forgot the original Q;
for my bees I haven't ever (I'm knocking on my head now) had much problem w/ varroa. I do see some, no more than 100 or so, on a bottom board from time to time, but even the "cleaned out" bees in front of my Long Hive I checked just yesterday were mite free, dead, but mite free and other wise, healthy "looking."
thomas